The subject invention relates to the field of osteogenic proteins and pharmaceutical formulations thereof. More particularly, the subject invention involves pharmaceutical formulations designed to sequester osteogenic protein in situ for a time sufficient to allow the protein to induce cartilage and/or bone formation.
Osteogenic proteins are those proteins capable of inducing, or assisting in the induction of, cartilage and/or bone formation. Many such osteogenic proteins have in recent years been isolated and characterized, and some have been produced by recombinant methods. For example, so-called bone morphogenic proteins (BMP) have been isolated from demineralized bone tissue (see e.g. Urist U.S. Pat. No. 4,455,256); a number of such BMP proteins have been produced by recombinant techniques (see e.g. Wang et al. U.S. Pat. No. 4,877,864 and Wang et al. U.S. Pat. No. 5,013,549); a family of transforming growth factors (TGF-.alpha. and TGF-.beta.) has been identified as potentially useful in the treatment of bone disease (see e.g. Derynck et al., EP 154,434); a protein designated Vgr-1 has been found to be expressed at high levels in osteogenic cells (see Lyons et al. (1989) Proc. Nat'l. Acad. Sci. USA 86, 4554-4558); and proteins designated OP-1, COP-5 and COP-7 have purportedly shown bone inductive activity (see oppermann, et al. U.S. Pat. No. 5,001,691).
Various attempts have been made at developing formulations designed to deliver osteogenic proteins to a site where induction of bone formation is desired. For example, certain polymeric matrices such as acrylic ester polymer (Urist, U.S. Pat. No. 4,526,909) and lactic acid polymer (Urist, U.S. Pat. No. 4,563,489) have been utilized, but these formulations do not sequester the osteogenic protein for a time sufficient to optimally induce bone formation, and further have been found to erode too slowly for optimal bone formation.
A biodegradable matrix of porous particles for delivery of an osteogenic protein designated as OP is disclosed in Kuberasampath, U.S. Pat. No. 5,108,753. While U.S. Pat. No. 5,108,753 discloses that a successful carrier for OP must bind the protein, act as a slow release delivery system, accommodate each step of the cellular response during bone development, and protect the protein from nonspecific proteolysis, no formulations are suggested which contain components that specifically sequester the OP at the site where bone formation is desired.
Ron et al., U.S. Pat. No. 5,171,579 discloses that the average surface area per porous particle is critical to optimize bone formation.
Okada et al., U.S. Pat. No. 4,652,441, U.S. Pat. No. 4,711,782, U.S. Pat. No. 4,917,893 and U.S. Pat. No. 5,061,492 and Yamamoto et al., U.S. Pat. No. 4,954,298 disclose a prolonged-release microcapsule comprising a polypeptide drug and a drug-retaining substance encapsulated in an inner aqueous layer surrounded by a polymer wall substance in an outer oil layer. Although bone morphogenic protein is listed as a polypeptide capable of such a formation, microencapsulation of osteogenic proteins prevents controlled release of such protein sufficient for optimal bone formation.
Yamazaki et al., Clin. Orthop. and Related Research, 234:240-249 (1988) disclose the use of implants comprising 1 mg of bone morphogenetic protein purified from bone and 5 mg of Plaster of Paris. U.S. Pat. No. 4,645,503 discloses composites of hydroxyapatite and Plaster of Paris as bone implant materials.
Collagen matrices have also been used as delivery vehicles for osteogenic proteins (see e.g. Jeffries, U.S. Pat. No. 4,394,370), but collagen frequently causes undesirable antigenic reactions in patients. Therefore, there remains a need for a pharmaceutical formulation capable of sequestering osteogenic proteins at a site where induction of bone formation is desired for a time sufficient to allow safe, effective induction of such bone formation.